Photoacid generator

ABSTRACT

The present invention relates to a novel photoacid generator compound cation, comprising an element having for 92 eV photons (extreme ultraviolet (EUV)) an absorption cross section of at least 0.5×107·cm2/mol; having at least two stable oxidation states; and selected from the elements of group 1 to group 15 of the periodic table of the elements. Additionally, the present invention relates to a photoacid generator comprising said photoacid generator compound cation and an anion. Furthermore, the present invention aims to provide a photoresist composition comprising said photoacid generator and an acid labile polymer. Finally, the present invention relates to a method of generating an acid using the photoresist composition and a method of forming a patterned materials feature on a substrate.

BACKGROUND

The present invention relates to the field of photoacid generators(PAGs). More specifically, the present invention relates to a newphotoacid generator for chemically amplified photoresists for EUVlithography.

Photoresists are photosensitive films for transfer of patterns to asubstrate. They form negative or positive patterns. After coating aphotoresist on a substrate, a source of activating energy, such asultraviolet light, is used to project a patterned mask or reticle,typically using a so-called stepper and a 4× reduction lens assembly,onto the coating to form a latent pattern in the photoresist coating.The mask defines the pattern desired to be transferred to the underlyingsubstrate.

Chemical amplification-type photoresists have proven to be useful inachieving high sensitivity in processes for forming patterns with smallfeature sizes in semiconductor manufacturing. These photoresists areprepared by blending a photoacid generator with a polymer matrix havingacid labile structures. According to the reaction mechanism of such aphotoresist, the photoacid generator generates acid when it isirradiated by the light source, and the main chain or branched chain ofthe polymer matrix in the exposed or irradiate portion reacts with thegenerated acid and is decomposed or cross-linked, so that the polarityof the polymer is altered. This alteration of polarity results in asolubility difference in the developing solution between the irradiatedexposed area and the unexposed area, thereby forming a positive ornegative pattern of a mask on the substrate.

Extreme ultraviolet (EUV) lithography is being used as one essentialtechnology for semiconductor manufacturing of next generation devices.EUV lithography is a technology platform that uses an EUV ray having awavelength of about 13.5 nm, which corresponds to an energy of about 92eV, as an exposure light source. With the help of the EUV lithography,patterns with very small feature sizes (e.g., patterns having a width orcritical dimension of less than or equal to about 20 nm) may be formedin an exposure process during a manufacturing of a semiconductor device.

Currently, photoresists for EUV lithography of the 7-nm and 5-nmtechnology nodes are polymer-based chemically amplified photoresists.These photoresist platforms comprise the following components:

-   -   (1) Photoacid generator: The PAG decomposes upon ultraviolet        (UV) exposure; an acid is generated along with degradation        products. Commonly used PAGs are based on sulfonium salts, for        example, triphenylsulfonium triflate. Upon UV exposure, the        sulphur-carbon (S—C) bond in the sulfonium salts undergoes        radical cleavage and an acid is generated.    -   (2) Acid-labile polymer: The acid-labile protection group of        this polymer can be removed by an acid. The thereby generated        compounds are alkali-soluble or volatile.

A key metric of the photoresist is its sensitivity. Sensitivity is theUV dose that is required to print a feature in the photoresist.Currently available chemically amplified photoresists for EUVlithography have generally a too low sensitivity. The material'stoxicity and chemical waste are in focus too. Currently availablechemically amplified photoresists for EUV lithography have generally amaterial's toxicity and chemical waste pain-point.

Inorganic photoresists based on metal oxides have been disclosed. Thisphotoresist platform comprises organotin clusters. Upon EUV exposure theSn-C bonds dissociate and the inorganic SnOx clusters crosslink. Thisleads to a change of solubility. The not exposed material is soluble inalkaline solvents whereas the exposed material is not. While inorganicphotoresists for EUV lithography have generally a high sensitivity,mitigating process-integration risks is challenging: the industry isreluctant to change the chemically amplified photoresists platforms.

In some instances, incorporation of In, Sn, Sb, Te, Tl, Pb, Bi, and Poin an organometallic compound is possible. Said “passive” organometalliccomponent can be admixed to chemically amplified photoresists for EUVlithography to increase the sensitivity in the EUV. The increase ofsensitivity in the EUV is however modest, because said “passive”organometallic component is not part of the chemically amplifiedphotoresists' PAG, which actively participates in the EUV-photon inducedchemical reactions.

In other instances, a radiation-sensitive composition can be used in EUVlithography, and includes a first polymer and a solvent. The firstpolymer includes a first structural unit including: at least one metalatom; and at least one carbon atom that each bonds to the metal atom bya chemical bond. The metal atom is preferably Ge, Sn, and Pb, which isincorporated in the acid-labile polymer of the photoresist. The increaseof sensitivity in the EUV is however modest, because said “passive”organometallic component is not part of the chemically amplifiedphotoresists' PAG, which actively participates in the EUV-photon inducedchemical reactions.

Other photoresists for EUV lithography include a polymer with onerepeating unit and an absorbing unit. In the acid-labile polymer Bi, Co,Fe, Ge, and P are incorporated. The increase of sensitivity in the EUVis however modest, because said “passive” organometallic component isnot part of the chemically amplified photoresists' PAG, which activelyparticipates in the EUV-photon induced chemical reactions.

The foregoing indicates a need for chemically amplified photoresists forEUV lithography having a high sensitivity and posing a limitedprocess-integration risk. Additionally, there is a need for chemicallyamplified photoresists which have a low material's toxicity and chemicalwaste.

SUMMARY

To achieve these and other advantages, and in accordance with thepurpose of the present invention as embodied and broadly describedherein, the invention comprises a novel photoacid generator, inparticular a photoacid generator compound cation, comprising an elementthat (i) has a high absorption cross section for photons in the EUV;(ii) has at least two stable oxidations states; and (iii) is selectedfrom the elements of group 1 to group 15 of the periodic table ofelements, preferably the elements indium (In), tin (Sn), antimony (Sb),thallium (Tl), lead (Pb), or bismuth (Bi). The photoacid generator'scompound cation molecular structure is chosen such that upon EUVexposure and In—C, Sn—C, Sb—C, Tl—C, Pb—C, or Bi—C bond radicalcleavage, the generated intermediate radicals R_(n-1)In⁺▪, R_(n-1)Sn⁺▪,R_(n-1)Sb⁺▪, R_(n-1)Tl⁺▪, R_(n-1)Pb⁺▪, or R_(n-1)Bi⁺▪, where “▪”indicates a radical and n=2 for the In and Tl compounds, n=3 for the Snand Pb compounds, and n=4 for the Sb and Bi compounds, are stabilized bygroups R. When the reaction is completed, a proton H⁺ is released alongwith degradation products, in which In, Sn, Sb, Tl, Pb, or Bi are in areduced oxidation state. The proton H⁺ combines with the photoacidgenerator's anion to form the Br∅nsted acid (or, in some cases, a Lewisacid) that further participates in the photolithography process. Thepresent invention comprises the formulation and use of photoresistsemploying these PAGs that are optimized for absorption characteristicsrequired for EUV photons. Incorporation of these PAGs can increase thesensitivity or photospeed of chemical amplified photoresists for EUVlithography.

In a first aspect, the present invention relates to a photoacidgenerator compound cation of the general formula (I)

R_(n)−X⁺  (I)

-   -   wherein    -   X represents an element    -   (i) having for 92 eV photons (extreme ultraviolet (EUV)) an        absorption cross section of at least 0.5×10⁷·cm²/mol;    -   (ii) having at least two stable oxidation states; and    -   (iii) selected from the elements of group 1 to group 15 of the        periodic table of the elements; R represents a linear or        branched or a cyclic unsubstituted or substituted alkyl group        having 1 to 20 carbon atoms; or an unsubstituted or substituted        aryl group having 3 to 30 carbon atoms;    -   or an unsubstituted or substituted unsaturated or saturated        heterocyclic group having a 3 to 30 membered ring; or        derivatives thereof;    -   wherein the R groups are either separated from each other or at        least two R groups are linked with each other; and    -   n is 2 to 5.

In another aspect, the present invention relates to a photoacidgenerator comprising the photoacid generator compound cation accordingto the present invention and an anion.

In another aspect, the present invention relates to a photoresistcomposition comprising

-   -   (a) a photoacid generator according to the present invention;        and    -   (b) an acid labile polymer.

In a further aspect, the present invention relates to a method forgenerating an acid, comprising the steps of: applying a photoresistcomposition according to the present invention to a substrate, thephotoresist composition containing a photoacid generator according tothe present invention, and irradiating the photoresist composition withan energy ray to cause the photoacid generator to generate an acid.

Finally, in a still further aspect, the present invention relates to amethod of forming a patterned materials feature on a substrate,comprising the steps of: providing a material surface on a substrate;forming a layer of the photoresist composition according to the presentinvention over said material surface; patternwise irradiating thephotoresist layer with an energy ray thereby creating a pattern ofradiation-exposed regions in said photoresist layer; selectivelyremoving portions of said photoresist layer to form exposed portions ofsaid material surface; and etching or ion implanting said exposedportions of said material, thereby forming said patterned materialfeature.

The present invention provides a new photoacid generator compound cationand a photoacid generator, that have a high absorption cross section forphotons in the EUV to increase the sensitivity of chemical amplifiedphotoresists for EUV lithography.

The chemically amplified photoresists for EUV lithography that comprisethe photoacid generator compound cation and the photoacid generatordescribed herein, also pose limited process-integration risks becausethe process flow in the fab's photobay is unchanged. Some embodimentshave a material's toxicity and chemical waste advantage.

Various variants provide a photoacid generator compound cation, aphotoacid generator, a photoresist composition and methods, as describedby the subject matter of the independent claims. Advantageous variantsare described in the dependent claims. Embodiments of the presentinvention can be freely combined with each other if they are notmutually exclusive.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described, byway of example only, with reference to the following drawings, in which:

FIG. 1 displays the photo absorption cross-section μ_(a) at 92 eV of allnaturally occurring elements.

FIG. 2 displays preferred PAG cations, in accordance with an embodimentof the present invention:

-   -   (a) PAG cation triphenyltin (Ph₃Sn⁺, with Sn(IV));    -   (b) PAG cation tetraphenylantimony (Ph₄Sb⁺, with Sb(V));    -   (c) PAG cation tetraphenylbismuth (Ph₄Bi⁺, with Bi(V));    -   (d) PAG cation 2,2′-biphenylylene-phenyltin (with Sn(IV));    -   (e) PAG cation 2,2′-biphenylylene-diphenylantimony (with Sb(V));        and    -   (f) PAG cation 2,2′-biphenylylene-diphenylbismuth (with Bi(V)).

FIG. 3 shows

-   -   (a) PAG cation triphenyltin (Ph₃Sn⁺, with Sn(IV)), Sn—C radical        bond cleavage and intermediate radicals (Ph▪ and Ph₂Sn⁺▪), and        proton H⁺ release and degradation product with Sn(II) according        to the present invention;    -   (b) PAG cation tetraphenylantimony (Ph₄Sb⁺, with Sb(V)), Sn—C        radical bond cleavage and intermediate radicals (Ph▪ and        Ph₃Sb⁺▪), and proton H⁺ release and degradation product with        Sb(III) according to the present invention;    -   (c) PAG cation tetraphenylbismuth (Ph₄Bi⁺, with Bi(V)), Bi—C        radical bond cleavage and intermediate radicals (Ph▪ and        Ph₃Bi⁺▪), and proton H⁺ release and degradation product with        Bi(III) according to the present invention; and    -   (d) for reference only: PAG cation triphenylsulfonium (Ph₃S⁺,        with Sn(IV)), S—C radical bond cleavage and intermediate        radicals (Ph▪ and Ph₂S⁺▪), and proton H⁺ release and degradation        product with S(II), in accordance with an embodiment of the        present invention.

FIG. 4 displays

-   -   (a) PAG triphenyltin chloride decomposition and HCl acid        generation;    -   (b) PAG tetraphenylantimony chloride decomposition and HCl acid        generation;    -   (c) PAG tetraphenylbismuth chloride decomposition and HCl acid        generation; and    -   (d) for reference only: PAG triphenylsulfonium chloride        decomposition and HCl acid generation, in accordance with an        embodiment of the present invention.

FIG. 5 displays

-   -   (a) PAG triphenyltin camphorsulfonate decomposition and        camphorsulfonic acid generation;    -   (b) PAG tetraphenylantimony camphorsulfonate decomposition and        camphorsulfonic acid generation; and    -   (c) PAG tetraphenylbismuth camphorsulfonate decomposition and        camphorsulfonic acid generation, in accordance with an        embodiment of the present invention.

FIG. 6 shows preferred fluorine-free PAGs, in accordance with anembodiment of the present invention:

-   -   (a) 2,2′-biphenylylene-diphenylbismuth camphorsulfonate; and    -   (b) 2,2′-biphenylylene-diphenylbismuth p-toluenesulfonate, in        accordance with an embodiment of the present invention.

FIG. 7 displays preferred fluorinated PAGs according to the presentinvention:

-   -   (a) 2,2′-biphenylylene-diphenylbismuth trifluormethanesulfonate;    -   (b) 2,2′-biphenylylene-diphenylbismuth        perfluoro-1-butanesulfonate;    -   (c) 2,2′-biphenylylene-diphenylbismuth hexafluorophosphate;    -   (d) 2,2′-biphenylylene-diphenylbismuth        tetrakis(pentafluorophenyl)borate;    -   (e) 2,2′-biphenylylene-diphenylbismuth        tris(trifluoromethanesulfonyl)methide;    -   (f) 2,2′-biphenylylene-diphenylbismuth        hexafluoropropane-1,3-disulfonimide;    -   (g) 2,2′-biphenylylene-diphenylbismuth        bis(trifluoromethanesulfonyl)amide;    -   (h) bis(2,2′-biphenylylene-diphenylbismuth)        perfluorobutane-1,4-disulfonate; and    -   (i) 2,2′-biphenylylene-diphenylbismuth        2-(trifluoromethyl)benzenesulfonate, in accordance with an        embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention recognize a need for chemicallyamplified photoresists for EUV lithography having a high sensitivity andposing a limited process-integration risk. Additionally, there is a needfor chemically amplified photoresists which have a low material'stoxicity and chemical waste. Accordingly, an object of the presentinvention is to provide a new photoacid generator compound cation and aphotoacid generator, and a photoresist composition that comprises saidnew photoacid generator, that increase the sensitivity of chemicallyamplified photoresists for EUV lithography and which pose limitedprocess-integration risks. The present invention further aims to providea photoacid generator that has a material's toxicity and chemical wasteadvantage. In particular, embodiments of the present invention providean improved a photoacid generator comprising a new photoacid generatorcompound cation, and a photoresist composition, comprising saidphotoacid generator compound. Finally, the present invention relates toa method of generating an acid using said photoresist composition and amethod of forming a patterned materials feature on a substrate.

The descriptions of the various embodiments of the present inventionwill be presented for purposes of illustration, but are not intended tobe exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

Unless otherwise stated, the following terms used in this application,including the specification and claims, have the definitions givenbelow. It must be noted that, as used in the specification and theappended claims, the singular forms “a,” “an,” and “the” include pluralreferents unless the context clearly dictates otherwise.

As used herein, the term “moiety” refers to a specific segment orfunctional group of a molecule. Chemical moieties are often recognizedchemical entities embedded in or appended to a molecule.

As used herein the term “aliphatic” encompasses the terms alkyl,alkenyl, alkynyl, each of which being optionally substituted as setforth below.

As used herein, an “alkyl” group refers to a saturated aliphatichydrocarbon group containing from 1 to 20 (e.g., 2 to 18, 3 to 18, 1 to8, 1 to 6, 1 to 4, or 1 to 3) carbon atoms. An alkyl group can bestraight, branched, cyclic or any combination thereof. Examples of alkylgroups include, but are not limited to, methyl, ethyl, propyl,isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-heptyl,or 2-ethylhexyl. An alkyl group can be substituted (i.e., optionallysubstituted) with one or more substituents or can be multicyclic as setforth below.

Unless specifically limited otherwise, the term “alkyl,” as well asderivative terms such as “alkoxy” and “thioalkyl,” as used herein,include within their scope, straight chain, branched chain, and cyclicmoieties.

As used herein, an “alkenyl” group refers to an aliphatic carbon groupthat contains from 2 to 20 (e.g., 2 to 18, 2 to 8, 2 to 6, or 2 to 4)carbon atoms and at least one double bond. Like an alkyl group, analkenyl group can be straight, branched or cyclic or any combinationthereof

Examples of an alkenyl group include, but are not limited to, allyl,isoprenyl, 2-butenyl, and 2-hexenyl. An alkenyl group can be optionallysubstituted with one or more substituents as set forth below.

As used herein, an “alkynyl” group refers to an aliphatic carbon groupthat contains from 2 to 20 (e.g., 2 to 8, 2 to 6, or 2 to 4) carbonatoms and has at least one triple bond. An alkynyl group can bestraight, branched or cyclic or any combination thereof. Examples of analkynyl group include, but are not limited to, propargyl and butynyl. Analkynyl group can be optionally substituted with one or moresubstituents as set forth below.

As used herein, the term “alicyclic” refers to an aliphatic ringcompound or group comprising at least three carbon atoms and the bondsbetween pairs of adjacent atoms may all be of the type designated singlebonds (involving two electrons), or some of them may be double or triplebonds (with four or six electrons, respectively).

A “halogen” is an atom of the group 17 of the periodic table ofelements, which includes fluorine, chlorine, bromine, and iodine.

As used herein, an “aryl” group refers to an aromatic ring compound orgroup having 3 to 30 carbon atoms and used alone or as part of a largermoiety as in “aralkyl,” “aralkoxy,” or “aryloxyalkyl” and refers tomonocyclic (e.g., phenyl); bicyclic (e.g., indenyl, naphthalenyl,tetrahydronaphthyl, or tetrahydroindenyl); and tricyclic (e.g.,fluorenyl, tetrahydrofluorenyl, tetrahydroanthracenyl, or anthracenyl)ring systems in which the monocyclic ring system is aromatic or at leastone of the rings in a bicyclic or tricyclic ring system is aromatic. Thebicyclic and tricyclic groups include benzofused 2 to 3 memberedcarbocyclic rings. For example, a benzofused group includes phenyl fusedwith two or more C₄ to C₈ carbocyclic moieties. An aryl is optionallysubstituted with one or more substituents as set forth below.

As used herein, an “aralkyl” or “arylalkyl” group refers to an alkylgroup (e.g., a C₁ to C₄ alkyl group) that is substituted with an arylgroup. Both “alkyl” and “aryl” have been defined above. An example of anaralkyl group is benzyl. An aralkyl is optionally substituted with oneor more substituents as set forth below.

As used herein, a “cycloalkyl” group refers to a saturated carbocyclicmono- to pentacyclic (fused or bridged) ring of 3 to 20 (e.g., 5 to 20)carbon atoms. Examples of cycloalkyl groups include cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, norbornyl,cubyl, octahydro-indenyl, decahydro-naphthyl, bicyclo[3.2.1]octyl,bicyclo[2.2.2]octyl, bicyclo[3.3.1]nonyl, bicyclo[3.3.2]decyl,bicyclo[2.2.2]octyl, adamantyl, azacycloalkyl, or((aminocarbonyl)cycloalkyl) cycloalkyl.

As used herein, the term “heteroaryl” group refers to a monocyclic,bicyclic, or tricyclic ring system having 3 to 30 ring atoms wherein oneor more of the ring atoms is a heteroatom (e.g., N, O, S, orcombinations thereof) and in which the monocyclic ring system isaromatic or at least one of the rings in the bicyclic or tricyclic ringsystems is aromatic. A heteroaryl group includes a benzofused ringsystem having 2 to 3 rings. For example, a benzofused group includesbenzo fused with one or two 4 to 8 membered heterocycloaliphaticmoieties (e.g., indolizyl, indolyl, isoindolyl, 3H-indolyl, indolinyl,benzo[b]furyl, benzo[b]thiophenyl, quinolinyl, or isoquinolinyl). Someexamples of heteroaryl are azetidinyl, pyridyl, 1H-indazolyl, furyl,pyrrolyl, thienyl, thiazolyl, oxazolyl, imidazolyl, tetrazolyl,benzofuryl, isoquinolinyl, benzthiazolyl, xanthene, thioxanthene,phenothiazine, dihydroindole, benzo[1,3]dioxole, benzo[b]furyl,benzo[b]thiophenyl, indazolyl, benzimidazolyl, benzthiazolyl, puryl,cinnolyl, quinolyl, quinazolyl, cinnolyl, phthalazyl, quinazolyl,quinoxalyl, isoquinolyl, 4H-quinolizyl, benzo-1,2,5-thiadiazolyl, or1,8-naphthyridyl.

Without limitation, monocyclic heteroaryls include furyl, thiophenyl,2H-pyrrolyl, pyrrolyl, oxazolyl, thazolyl, imidazolyl, pyrazolyl,isoxazolyl, isothiazolyl, 1,3,4-thiadiazolyl, 2H-pyranyl, 4-H-pranyl,pyridyl, pyridazyl, pyrimidyl, pyrazolyl, pyrazyl, or 1,3,5-triazyl.Monocyclic heteroaryls are numbered according to standard chemicalnomenclature.

Without limitation, bicyclic heteroaryls include indolizyl, indolyl,isoindolyl, 3H-indolyl, indolinyl, benzo[b]furyl, benzo[b]thiophenyl,quinolinyl, isoquinolinyl, indolizyl, isoindolyl, indolyl,benzo[b]furyl, bexo[b]thiophenyl, indazolyl, benzimidazyl,benzthiazolyl, purinyl, 4H-quinolizyl, quinolyl, isoquinolyl, cinnolyl,phthalazyl, quinazolyl, quinoxalyl, 1,8-naphthyridyl, or pteridyl.Bicyclic heteroaryls are numbered according to standard chemicalnomenclature.

A heteroaryl is optionally substituted with one or more substituents asis set forth below.

A “heteroarylalkyl” group, as used herein, refers to an alkyl group(e.g., a C₁ to C₄ alkyl group) that is substituted with a heteroarylgroup. Both “alkyl” and “heteroaryl” have been defined above. Aheteroarylalkyl is optionally substituted with one or more substituentsas is set forth below.

As used herein, an “acyl” group refers to a formyl group or R^(X)—C(O)-(such as -alkyl-C(O)-, also referred to as “alkylcarbonyl”) where“alkyl” has been defined previously.

As used herein, the term “acyloxy” includes straight-chain acyloxy,branched-chain acyloxy, cycloacyloxy, cyclic acyloxy,heteroatom-unsubstituted acyloxy, heteroatom-substituted acyloxy,heteroatom-unsubstituted C_(n)-acyloxy, heteroatom-substitutedC_(n)-acyloxy, alkylcarbonyloxy, arylcarbonyloxy, alkoxycarbonyloxy,aryloxycarbonyloxy, and carboxylate groups.

As used herein, an “alkoxy” group refers to an alkyl-O- group where“alkyl” has been defined previously.

As used herein, a “carboxy” group refers to —COOH, —COOR^(X), —OC(O)H,—OC(O)R^(X) when used as a terminal group; or —OC(O)- or —C(O)O- whenused as an internal group.

As used herein, “alkoxycarbonyl” means —COOR, where R is alkyl asdefined above, e.g., methoxycarbonyl, ethoxycarbonyl, and the like.

As used herein, a “sulfinyl” group refers to —S(O)—R^(X) when usedterminally or S(O)- when used internally.

As used herein, a “sulfonyl” group refers to —S(O)₂—R^(X) when usedterminally or —S(O)₂- when used internally.

The term “alkylthio” includes straight-chain alkylthio, branched-chainalkylthio, cycloalkylthio, cyclic alkylthio, heteroatom-unsubstitutedalkylthio, heteroatom-substituted alkylthio, heteroatom-unsubstitutedC_(n)-alkylthio, and heteroatom-substituted C_(n)-alkylthio. In certainembodiments, lower alkylthios are contemplated.

As used herein, the term “amine” or “amino” includes compounds where anitrogen atom is covalently bonded to at least one carbon or heteroatom.The term “amine” or “amino” also includes —NH₂ and also includessubstituted moieties. The term includes “alkyl amino” which comprisesgroups and compounds wherein the nitrogen is bound to at least oneadditional alkyl group. The term includes “dialkyl amino” groups whereinthe nitrogen atom is bound to at least two additional independentlyselected alkyl groups. The term includes “arylamino” and “diarylamino”groups wherein the nitrogen is bound to at least one or twoindependently selected aryl groups, respectively.

The term “haloalkyl” refers to alkyl groups substituted with from one upto the maximum possible number of halogen atoms. The terms “haloalkoxy”and “halothioalkyl” refer to alkoxy and thioalkyl groups substitutedwith from one up to five halogen atoms.

The phrase “optionally substituted” is used interchangeably with thephrase “substituted or unsubstituted.” As described herein, compounds ofthe present disclosure can optionally be substituted with one or moresubstituents, such as are illustrated generally above, or as exemplifiedby particular classes, subclasses, and species of the presentdisclosure. As described herein any of the above moieties or thoseintroduced below can be optionally substituted with one or moresubstituents described herein. Each substituent of a specific group isfurther optionally substituted with one to three of halo, cyano,oxoalkoxy, hydroxy, amino, nitro, aryl, haloalkyl, and alkyl. Forinstance, an alkyl group can be substituted with alkyl sulfonyl and thealkyl sulfonyl can be optionally substituted with one to three of halo,cyano, oxoalkoxy, hydroxy, amino, nitro, aryl, haloalkyl, and alkyl.

In general, the term “substituted,” whether preceded by the term“optionally” or not, refers to the replacement of hydrogen radicals in agiven structure with the radical of a specified substituent. Specificsubstituents are described above in the definitions and below in thedescription of compounds and examples thereof. Unless otherwiseindicated, an optionally substituted group can have a substituent ateach substitutable position of the group, and when more than oneposition in any given structure can be substituted with more than onesubstituent selected from a specified group, the substituent can beeither the same or different at every position. A ring substituent, suchas a heterocycloalkyl, can be bound to another ring, such as acycloalkyl, to form a spiro-bicyclic ring system, e.g., both rings shareone common atom. As one of ordinary skill in the art will recognize,combinations of substituents envisioned by this present disclosure arethose combinations that result in the formation of stable or chemicallyfeasible compounds.

Modifications or derivatives of the compounds disclosed throughout thisspecification are contemplated as being useful with the methods andcompositions of the present disclosure. Derivatives may be prepared andthe properties of such derivatives may be assayed for their desiredproperties by any method known to those of skill in the art. In certainaspects, “derivative” refers to a chemically modified compound thatstill retains the desired effects of the compound prior to the chemicalmodification.

The photoacid generator compound cation according to the presentdisclosure can be used as photoacid generator as will be explained inmore detail below. The term “photoacid generator” means a compoundcapable of producing an acid by decomposition of its chemical structurewhen irradiated with light.

Surprisingly, it has been discovered that the PAG compound cations ofthe present disclosure are characterized by excellent photo-reactivityfor EUV radiation.

The present invention provides photoacid generators to be formulatedinto polymer compositions that are useful in lithographic processes,especially when EUV radiation is used. In carrying out the presentinvention, conventional materials and processing techniques can beemployed and, hence, such conventional aspects are not set forth hereinin detail. For example, the selection of suitable acid labile polymers,base quenchers, and solvents is conducted in a conventional manner.

In one aspect, the present invention relates to a photoacid generatorcompound cation of the general formula (I)

R_(n)−X⁺  (I)

-   -   wherein    -   X represents an element    -   (i) having for 92 eV photons (extreme ultraviolet (EUV)) an        absorption cross section of at least 0.5×10⁷·cm²/mol;    -   (ii) having at least two stable oxidation states; and    -   (iii) selected from the elements of group 1 to group 15 of the        periodic table of the elements; R represents a linear or        branched or a cyclic unsubstituted or substituted alkyl group        having 1 to 20 carbon atoms; or an unsubstituted or substituted        aryl group having 3 to 30 carbon atoms; or an unsubstituted or        substituted unsaturated or saturated heterocyclic group having a        3 to 30 membered ring; or derivatives thereof;    -   wherein the R groups are either separated from each other or at        least two R groups are linked with each other; and    -   n is 2 to 5.

The photoacid generator compound cation of the general formula (I) ischaracterized in that it comprises an element X that has for 92 eVphotons an absorption cross section of at least 0.5×10⁷·cm²/mol.

FIG. 1 displays the photo absorption cross-section μ_(a) at 92 eV of allnaturally occurring elements. The absorption of photons in a layer ofthickness d is given by 1—exp (−n μ_(a) d), where n is the number ofatoms per unit volume in the layer.

In order to devise photoacid generators that can be used to increase thesensitivity of chemically amplified photoresists for EUV lithography, itis crucial to understand and to appreciate the microscopic mechanismsthat cause photon absorption events and that cause photoacid generatordecomposition in the EUV, in contrast to in the DUV.

The DUV (193 nm or 248 nm, 6 eV or 5 eV, respectively) photon absorptionis determined by the molecular orbitals of the photoresist material. Theabsorbed photons can directly and selectively cause resonant electronictransition in the photoacid generator, resulting in the generation of anacid. The sensitivity of chemically amplified photoresists for DUVlithography can be increased by adjusting the molecular structure of thephotoacid generator.

By contrast, the EUV (13.5 nm, 92 eV, soft X-ray) photon absorption isdetermined by the atomic composition of the photoresist material, i.e.,the molecular structure is essentially not relevant.

DUV photoresist platforms are mainly composed of light elements such asH, C, O, F, and S, which all have for 92 eV photons a low absorptioncross section. This limits their EUV performance.

To increase the chemically amplified photoresists' 92 eV photonabsorption cross section, elements that have a large absorption crosssection at this photon energy must be added directly to the photoresistcomposition.

Embodiments of the present invention recognize, surprisingly, that inEUV lithograph the absorbed photon ionizes an atom in the photoresist.The photoelectron (about 80 eV) subsequently causes a cascade ofnonradiative processes. Inelastic scattering from the valence electronsis the major loss mechanism for incident electrons at this energy range.The electron's inelastic scattering mean-free-path is in the order of 1Å at 80 eV to 10 Å at 10 eV. The lower-energy electrons (<10 eV) causeelectronic transitions in the photoacid generator, resulting in thegeneration of the acid.

Furthermore, it was realized that, because the electrons have a shortinelastic scattering mean-free-path, it is advantageous to incorporatethese elements directly in the photoacid generator to ensure thatsecondary electrons are present in the proximity of the photoacidgenerator. This is an advantage over the prior art, for example, US20190310552 A1 or US 20200103754 A1, where the metal atom isincorporated in the acid-labile polymer of the photoresist, or US20200041901 A1 where the metal atom is incorporated in a “passive”compound admixed to the photoresist.

In order to advantageously increase the 92 eV absorption in thechemically amplified photoresist, the element of the photoacid generatorcompound cation must have an absorption cross section for 92 eV photonsof at least 0.5×10⁷·cm²/mol. In a preferred variant of the presentinvention, the element of the photoacid generator compound cation musthave an absorption cross section for 92 eV photons of at least0.75×10⁷·cm²/mol. In a particularly preferred variant of the presentinvention, the element of the photoacid generator compound cation musthave an absorption cross section for 92 eV photons of at least1.0×10⁷·cm²/mol.

Additionally, the element to be successfully incorporated in thephotoacid generator, in particular in the photoacid generator compoundcation, must have at least two stable oxidation states that areseparated by two elementary charges.

In a preferred variant, the elements advantageously incorporated in thephotoacid generator have the oxidations states 1+and 3+; 2+and 4+; 3+and5+; or 4+and 6+.

As can be derived from FIG. 1, the elements having an absorption crosssection for 92 eV photons of at least 0.5×10⁷·cm²/mol are preferablyselected from the group consisting of the elements In, Sn, Sb, Tl, Pb,and Bi.

In a more preferred variant of the present invention, the elements ofthe photoacid generator compound cation having an absorption crosssection for 92 eV photons of at least 0.75×10⁷·cm²/mol are selected fromthe group consisting of In, Sn, Sb, Pb, and Bi.

In a particularly preferred variant of the present invention, theelements of the photoacid generator compound cation having an absorptioncross section for 92 eV photons of at least 1.0×10⁷·cm²/mol are selectedfrom the group consisting of In, Sn, Sb, and Bi.

The elements of the photoacid generator compound cation having the abovespecified absorption cross section for 92 eV photos result in a bettersensitivity, when incorporated directly in the photoacid generatoraccording to the present invention.

Additionally, the elements In, Sn, Sb, and Bi are particularly preferredunder toxicity consideration since organometallic compounds comprisingTl and Pb are toxic.

Additionally, the elements Sn, Sb, and Bi are particularly preferred incomparison to the element In since organometallic compounds comprisingIn exhibit at room temperature less stable photoreactions.

By contrast, the elements Te and Po belonging to the group 16 of theperiodic table of the elements, and, thus, not covered by the definitionof the element X of the general formula (I) of the present invention,are excluded since organometallic compounds comprising Te and Po areprohibitively toxic.

Elements with said at least two stable oxidation states include theelements In (oxidation states include 1+and 3+), Sn (oxidation statesinclude 2+and 4+), Sb (oxidation states include 3+and 5+), Tl (oxidationstates include 1+and 3+), Pb (oxidation states include 2+and 4+), and Bi(oxidation states include 3+and 5+). Preferred elements include Sn(oxidation states 2+and 4+), Sb (oxidation states 3+and 5+), and Bi(oxidation states 3+and 5+).

Moreover, the element X of the photoacid generator compound cation ofgeneral formula (I) according to the present invention is selected fromthe elements of group 1 to group 15 of the periodic table of theelements. Preferably, the element Xis selected from the elements ofgroup 13, 14, and 15 of the periodic table of the elements. The elementX of the photoacid generator compound cation of the general formula (I)of the present invention is not an element of the group 16 of theperiodic table of the elements, in particular is not Te or Po due totheir toxicity.

Hence, in a more preferred variant the element X of the photoacidgenerator compound cation of the general formula (I) which fulfil thethree requirements specified above, namely for 92 eV photons anabsorption cross section of at least 0.5×10⁷·cm²/mol, at least twostable oxidation states and selected from the elements of group 1 togroup 15 of the periodic table of the elements is selected from thegroup consisting of In, Sn, Sb, Tl, Pb, and Bi. In a particularpreferred variant the element X of the photoacid generator compoundcation of the general formula (I) is selected from the group consistingof Sn, Sb, and Bi.

The photoacid generator compound cation of the general formula (I)further comprises at least two organic group(s) R. The number of theorganic R group depends on the oxidation state of the element X in thegeneral formula (I). R in the general formula (I) represents a linear orbranched or a cyclic unsubstituted or substituted alkyl group having 1to 20 carbon atoms; or an unsubstituted or substituted aryl group having3 to 30 carbon atoms; or an unsubstituted or substituted unsaturated orsaturated heterocyclic group having a 3 to 30 membered ring; orderivatives thereof

With regard to the terms “unsubstituted or substituted aryl group”,“unsubstituted or substituted unsaturated or saturated heterocyclicgroup” or “derivatives”, reference is made to the above generaldefinitions.

Especially preferred, the linear or branched alkyl group is selectedfrom the group consisting of methyl, ethyl, butyl, pentyl, hexyl,heptyl, octyl, nonyl decyl, undecyl, dodecyl, tridecyl, tetradecyl,pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosayl andderivatives thereof; and/or the cyclic alkyl group is selected from thegroup consisting of cyclopentane, cyclohexane, cycloheptane, cyclooctaneand derivatives thereof; and/or the aryl group is selected from thegroup consisting of phenyl, naphthyl and derivatives thereof; and/or thesaturated or unsaturated heterocyclic group having one or twoheteroatoms is selected from the group consisting of pyrrolidine,pyrrole, tetrahydrofuran, furan, tetrahydrothiophene, thiophene,imidazolidine, imidazole, oxazolidine, oxyzole, thiazolidine, thiazole,dioxolane, dithiolane, piperidine, pyridine, tetrahydropyran, pyran,thiane, thiopyran, diazinane, diazine, in particular pyridazin(1,2-diazin), pyrimidine (1,3-diazin) and pyrazin (1,4-diazin),morpholine, oxazine, thiomorpholine, thiazine, dioxane, dioxine,dithiane, dithiin, quinolone, isoquinoline and derivatives thereof.

Modifications or derivatives of the compounds disclosed throughout thisspecification are contemplated as being useful with the methods andcompositions of the present disclosure. Derivatives may be prepared andthe properties of such derivatives may be assayed for their desiredproperties by any method known to those of skill in the art. In certainaspects, “derivative” refers to a chemically modified compound thatstill retains the desired effects of the compound prior to the chemicalmodification.

Due to their delocalized electrons, aryl groups or aromatic cycles andunsaturated heterocyclic groups, are more stable and, thus particularlypreferred as appropriate R group(s) in the general formula (I) of thephotoacid generator compound cation, compared for example to alkylgroups.

Aromatic groups such as phenyl, naphthyl, and their derivatives, andunsaturated heterocyclic groups such as pyridinyl, thiophenyl, and theirderivatives are particularly preferred in the photoacid generatorcompound cation according to the present invention.

In a preferred variant, the one or more organic group(s) R of thegeneral formula (I), namely the alkyl group or the aryl group or theheterocyclic group is/are optionally substituted. The phrase “optionallysubstituted” is used interchangeably with the phrase “substituted orunsubstituted.” As described herein, compounds of the present disclosurecan optionally be substituted with one or more substituents, such as areillustrated generally above, or as exemplified by particular classes,subclasses, and species of the present disclosure. As described hereinany of the above moieties or those introduced below can be optionallysubstituted with one or more substituents described herein. Eachsubstituent of a specific group is further optionally substituted withone to three of halo, cyano, oxoalkoxy, hydroxy, amino, nitro, aryl,haloalkyl, and alkyl. For instance, an alkyl group can be substitutedwith alkylsulfanyl and the alkylsulfanyl can be optionally substitutedwith one to three of halo, cyano, oxoalkoxy, hydroxy, amino, nitro,aryl, haloalkyl, and alkyl.

The term “substituted,” whether preceded by the term “optionally” ornot, refers to the replacement of hydrogen radicals in a given structurewith the radical of a specified substituent. Specific substituents aredescribed above in the definitions and below in the description ofcompounds. Unless otherwise indicated, an optionally substituted groupcan have a substituent at each substitutable position of the group, andwhen more than one position in any given structure can be substitutedwith more than one substituent selected from a specified group, thesubstituent can be either the same or different at every position. Aring substituent, such as a heterocycloalkyl, can be bound to anotherring, such as a cycloalkyl, to form a spiro-bicyclic ring system, e.g.,both rings share one common atom.

In a preferred variant, the one or more organic group(s) R of thegeneral formula (I), namely the alkyl group or the aryl group or theheterocyclic group, include(s) at least one substituent selected fromthe group consisting of halogen, hydroxyl, alkyl, alkoxy, aryl, aryloxy,nitro, and cyano.

The element X in the general formula (I) can either have two or more Rgroups which are identical or can have two or more R groups which aredifferent. In a preferred variant, the element X in the photoacidgenerator cation has identical R groups.

The at least two R groups of the photoacid generator compound cation ofthe general formula (I) are either separated from each other or the atleast two R groups are linked with each other. The term “separated fromeach other” means that the R groups are not interconnected or linkedwith each other. The term “at least two R groups are linked with eachother” means that two or even more than two R groups are linked witheach other or interconnected. In a preferred variant, the R groups ofthe photoacid generator compound cation of the general formula (I) areseparated from each other. In a particularly preferred variant, two Rgroups of the photoacid generator compound cation of the general formula(I) are linked with each other.

The bond between the at least two R groups can be a covalent bondbetween any of two C atoms of the two R groups. Alternatively, the atleast two R groups can be linked via a linking atom or linking group.The linking atom or linking group is preferably selected from the groupconsisting of —C—, —O—, —S—, —C(O)—, —S(O)-, and —S(O)₂-. In a preferredvariant according to the present invention, two of the R groups of theelement X of the photoacid generator cation of the general formula (I)are connected via a covalent bond between any two carbon atoms of thetwo R groups. If the at least two R groups are linked with each other, amulticycle ring is formed defined by the linkage of the two R groups andthe linkage of the two R groups to the element X of the photoacidgenerator cation of the general formula (I). The number of themulticycle ring depends on the linkage site or binding site between thefirst and second R group. Preferably, the multicycle ring is afour-membered ring, a five-membered ring, a six-membered ring, aseven-membered ring, etc. If the at least two linked R groups are phenylgroups, the ring formed by the linkage is a five-membered ring.Preferred PAG cations according to the present invention, in which two Rgroups are linked with each other with a covalent bond between two Catoms of the two R groups, are depicted in FIGS. 2(d) to (f).

The “n” in the general formula (I) represents an integer from 2 to 5,depending on the oxidation state of the element X. For an element X withthe following oxidation states, the following integer results:

-   -   oxidation states 1+ and 3+: n=2;    -   oxidation states 2+ and 4+: n=3;    -   oxidation states 3+ and 5+: n=4; and    -   oxidation states 4+ and 6+: n=5.

The photoacid generator compound cation according to the presentinvention is preferably selected from the group consisting of:

-   -   diphenylindium (Ph₂In⁺, with In(III)),    -   2,2′-biphenylylene-indium (with In(III))),    -   triphenyltin (Ph₃Sn⁺, with Sn(IV)),    -   2,2′-biphenylylene-phenyltin (with Sn(IV)),    -   tetraphenylantimony (Ph₄Sb⁺, with Sb(V)),    -   2,2′-biphenylylene-diphenylantimony (with Sb(V)),    -   diphenylthallium (Ph₂Tl⁺, with Tl(III)),    -   2,2′-biphenylylene-thallium (with Tl(III)),    -   triphenyllead (Ph₃Pb⁺, with Pb(IV)),    -   2,2′-biphenylylene-phenyllead (with Pb(IV)),    -   tetraphenylbismuth (Ph₄Bi⁺, with Bi(V)), and    -   2,2′-biphenylylene-diphenylbismuth (with Bi(V)).

The six specified compound cations triphenyltin,2,2′-biphenylylene-phenyltin, tetraphenylantimony,2,2′-biphenylylene-diphenylantimony, tetraphenylbismuth, and2,2′-biphenylylene-diphenylbismuth are shown in FIG. 2.

In a particular preferred variant, the photoacid generator compoundcation according to the present invention is selected from the groupconsisting of triphenyltin, 2,2′-biphenylylene-phenyltin,tetraphenylantimony, 2,2′-biphenylylene-diphenylantimony,tetraphenylbismuth, and 2,2′-biphenylylene-diphenylbismuth.

The photoacid generator compound cation's molecular structure is chosensuch that upon exposure by EUV radiation one or even more In—C, Sn—C,Sb—C, Tl—C, Pb—C, or Bi—C bond is/are radically cleaved. In a preferredvariant, one In—C, Sn—C, Sb—C, Tl—C, Pb—C, or Bi—C bond is radicallycleaved. Upon radical cleavage of the In—C, Sn—C, Sb—C, Tl—C, Pb—C, orBi—C bond, an intermediate radical R_(n-1)In⁺▪, R_(n-1)Sn⁺▪,R_(n-1)Sb⁺▪, R_(n-1)Tl⁺▪, R_(n-1)Pb⁺▪, or R_(n-1)Bi⁺▪, where “▪”indicates a radical and n=2 for the In and Tl compounds, n=3 for the Snand Pb compounds, and n=4 for the Sb and Bi compounds, is generated. Thecorresponding intermediate radicals are shown exemplary for Sn, Sb, andBi in FIG. 3:

-   -   (a) PAG cation triphenyltin (Ph₃Sn⁺, with Sn(IV)), Sn—C radical        bond cleavage and intermediate radicals (Ph▪ and Ph₂Sn⁺▪);    -   (b) PAG cation tetraphenylantimony (Ph₄Sb⁺, with Sb(V)), Sn—C        radical bond cleavage and intermediate radicals (Ph▪ and        Ph₃Sb⁺▪); and    -   (c) PAG cation tetraphenylbismuth (Ph₄Bi⁺, with Bi(V)), Bi—C        radical bond cleavage and intermediate radicals (Ph▪ and        Ph₃Bi⁺▪).

Next, the intermediate radical, such as R_(n-1)In⁺▪, Rn_(n-1)Pb⁺▪, andR_(n-1)Bi⁺▪, with n=2 for the In and Tl compounds, n=3 for the Sn and Pbcompounds, and n=4 for the Sb and Bi compounds, is stabilized by thegroup R (e.g., Ph). The stabilization mechanism is visualized exemplaryfor Sn, Sb, and Bi in FIG. 3.

When the reaction (i.e., radical cleavage and stabilization) iscompleted, a proton (H⁺) is released along with a degradation product inwhich In, Sn, Sb, Tl, Pb, or Bi is in a reduced oxidation state. Theoxidation state of In, Sn, Sb, Tl, Pb, and Bi must be reduced by twoelementary charges (see FIG. 3, Sn: 4+to 2+; Sb and Bi: 5+to 3+).

Due to their delocalized electrons, aryl groups or aromatic cycles orunsaturated heterocyclic groups are more stable and thus particularlysuitable as R groups, compared, for example, to alkyl groups. PreferredR groups include aromatic cycles such as phenyl, naphthyl or theirderivatives or unsaturated heterocycles such as pyrimidyl, thiophenyl ortheir derivatives.

The released proton (H⁺) combines with the photoacid generator's anion,as described in detail below, to form the Br∅nsted acid (or, in somecases, a Lewis acid), that further participates in the photolithographyprocess.

Surprisingly, the present invention provides a photoacid generatorcompound cation and a photoacid generator, comprising said photoacidgenerator compound cation, that have a high absorption cross section forphotons in the EUV to increase the sensitivity of chemical amplifiedphotoresists for EUV lithography.

Ab initio simulations, which are computational chemistry methods basedon quantum chemistry, of the photoreactions shown in FIG. 3, in gasphase, at 0 K, and at the Perdew-Burke-Esnzerof and double-zeta valencepolarisations (PBE/DZP) level of theory, were performed. For the firststep of the photodissociation for the Sn, Sb, and Bi compounds, reactionenergies of 76, 70, and 60 kcal/mol, respectively, were obtained. Forreference or contextual purposes only, for the prior art S compound, thereaction energy is 71 kcal/mol (Journal of Photopolymer Science andTechnology, 9, 587 (1996)). Hence, the Sn, Sb, and Bi compounds have adissociation energy which is similar to the dissociation energy of theprior art S compound. Hence, the Sn, Sb, and Bi compounds can be used inthe photoreactions shown in FIG. 3.

Additionally, ab initio simulations of the photoreactions shown in FIG.4, in gas phase, at 0 K, and at the PBE/DZVP level of theory, wereperformed. For the photoreactions for the Sn, Sb, and Bi compound,reaction energies of +29, −18, and −33 kcal/mol, respectively, wereobtained. For reference or contextual purposes only, for the prior art Scompound, the reaction energy is −36 kcal/mol. Thus, the Sb and Bicompounds have favorable reaction energies. The reaction energy of theBi compound is similar to the reaction energy of the prior art Scompound. The Sn compound has a positive reaction energy due to therelative instability of the Sn(II) compound compared to the Sn(IV)compound. Hence, the Sb and Bi compounds, and very likely the Sncompound, can be used in the photoreactions shown in FIG. 4.

Persons with an ordinary skill in the art will realize that ab initiosimulations of photoreactions of the Sn, Sb, and Bi compounds with otheranions, for example, ab initio simulations of photoreactions shown inFIG. 5, would yield similar respective reaction energies.

The above described ab initio simulations demonstrate that the preferredembodiments of the photoacid generator compound cation, namelytetraphenylantimony, tetraphenylbismuth, and very likely triphenyltin,can be used advantageously in photoreaction. Hence, due to saidadvantageous properties, the most preferred elements X in the photoacidgenerator compound cation according to the present invention areantimony, bismuth, and tin, and the most preferred groups R in thephotoacid generator compound cation according to the present inventionis phenyl.

However, persons with an ordinary skill in the art will realize that inthe photoreactions described in detail above also other, i.e., modified,photoacid generator compound cations according to the present inventionwith alternatives groups R, such as naphthyl or saturated or unsaturatedheterocyclic group, etc., as defined above, or with at least two Rgroups that are linked with each other via a covalent bond or a linkingatom or linking group between any of two carbon atoms of two R groups asdefined above, can be used.

In a most preferred variant, two of the R groups of the element X in thephotoacid generator cation are linked with each other, which influencesthe rotational degrees of freedom or resonance behavior of the photoacidgenerator compound cation, via a covalent bond between any of two Catoms of the two R groups. Hence, due to said advantageous properties,the most preferred photoacid generator compound cations according to thepresent invention are 2,2′-biphenylylene-diphenylantimony,2,2′-biphenylylene-diphenylbismuth, and 2,2′-biphenylylene-phenyltin.

The photoacid generator compound according to the present inventionfurther comprises an anion. The anion is a conventional or typical anionused for photoacid generators, and there are numerous derivatives taughtin the art.

Preferably, the photoacid generator according to the present inventionincludes a combination of the photoacid generator compound cationaccording to the present invention with known -fluorine-free anions suchas camphorsulfonate and p-toluenesulfonate, or known fluorinated anionssuch as trifluoromethanesulfonate, perfluoro-1-butanesulfonate,hexafluorophosphate, hexafluoroantimonate, tetrakis(pentafluorophenyl)borate, tris(trifluoromethanesulfonyl)methide,hexafluoropropane-1,3-disulfonimide, bis(trifluoromethenesulfonyl)amide,perfluorobutane-1,4-disulfonate, 2-(trifluoromethyl)benzenesulfonate andderivatives thereof

FIG. 6 depicts preferred embodiments of the photoacid generators on thebasis of the photoacid generator compound cation2,2′-biphenylylene-diphenylbismuth in combination with fluorine-freeanions:

-   -   (a) 2,2′-biphenylylene-diphenylbismuth camphorsulfonate; and    -   (b) 2,2′-biphenylylene-diphenylbismuth p-toluenesulfonate.

FIG. 7 depicts preferred embodiments of the photoacid generators on thebasis of the photoacid generator compound cation2,2′-biphenylylene-diphenylbismuth in combination with fluorinatedanions

-   -   (a) 2,2′-biphenylylene-diphenylbismuth trifluormethanesulfonate;    -   (b) 2,2′-biphenylylene-diphenylbismuth        perfluoro-1-butanesulfonate;    -   (c) 2,2′-biphenylylene-diphenylbismuth hexafluorophosphate;    -   (d) 2,2′-biphenylylene-diphenylbismuth        tetrakis(pentafluorophenyl)borate;    -   (e) 2,2′-biphenylylene-diphenylbismuth        tris(trifluoromethanesulfonyl)methide;    -   (f) 2,2′-biphenylylene-diphenylbismuth        hexafluoropropane-1,3-disulfonimide;    -   (g) 2,2′-biphenylylene-diphenylbismuth        bis(trifluoromethanesulfonyl)amide;    -   (h) bis(2,2′-biphenylylene-diphenylbismuth)        perfluorobutane-1,4-disulfonate; and    -   (i) 2,2′-biphenylylene-diphenylbismuth        2-(trifluoromethyl)benzenesulfonate.

In a more preferred variant, the photoacid generator according to thepresent invention is selected from the group consisting of:

-   -   triphenyltin camphorsulfonate,    -   triphenyltin p-toluenesulfonate,    -   triphenyltin trifluoromethenesulfonate,    -   triphenyltin perfluoro-1-butanesulfonate,    -   triphenyltin hexafluorophosphate,    -   triphenyltin hexafluoroantimonate,    -   triphenyltin tetrakis(pentafluorphenyl)borate,    -   triphenyltin tris(trifluoromethanesulfonyl)methide,    -   triphenyltin hexafluoropropane-1,3-disulfonimide,    -   triphenyltin bis(trifluoromethenesulfonyl)amide,    -   bis(triphenyltin) perfluorbutane-1,4-disulfonate,    -   triphenyltin 2-(trifluormethyl)benzenesulfonate,    -   2,2′-biphenylylene-phenyltin camphorsulfonate,    -   2,2′-biphenylylene-phenyltin p-toluenesulfonate,    -   2,2′-biphenylylene-phenyltin trifluoromethenesulfonate,    -   2,2′-biphenylylene-phenyltin perfluoro-1-butanesulfonate,    -   2,2′-biphenylylene-phenyltin hexafluorophosphate,    -   2,2′-biphenylylene-phenyltin hexafluoroantimonate,    -   2,2′-biphenylylene-phenyltin tetrakis(pentafluorphenyl)borate,    -   2,2′-biphenylylene-phenyltin        tris(trifluoromethanesulfonyl)methide,    -   2,2′-biphenylylene-phenyltin        hexafluoropropane-1,3-disulfonimide,    -   2,2′-biphenylylene-phenyltin bis(trifluoromethenesulfonyl)amide,    -   bis(2,2′-biphenylylene-phenyltin)        perfluorbutane-1,4-disulfonate,    -   2,2′-biphenylylene-phenyltin 2-(trifluormethyl)benzenesulfonate,    -   tetraphenylantimony camphorsulfonate,    -   tetraphenylantimony p-toluenesulfonate,    -   tetraphenylantimony trifluoromethenesulfonate,    -   tetraphenylantimony perfluoro-1-butanesulfonate,    -   tetraphenylantimony hexafluorophosphate,    -   tetraphenylantimony hexafluoroantimonate,    -   tetraphenylantimony tetrakis(pentafluorphenyl)borate,    -   tetraphenylantimony tris(trifluoromethanesulfonyl)methide,    -   tetraphenylantimony hexafluoropropane-1,3-disulfonimide,    -   tetraphenylantimony bis(trifluoromethenesulfonyl)amide,    -   bis(tetraphenylantimony) perfluorbutane-1,4-disulfonate,    -   tetraphenylantimony 2-(trifluormethyl)benzenesulfonate,    -   2,2′-biphenylylene-diphenylantimony camphorsulfonate,    -   2,2′-biphenylylene-diphenylantimony p-toluenesulfonate,    -   2,2′-biphenylylene-diphenylantimony trifluoromethenesulfonate,    -   2,2′-biphenylylene-diphenylantimony perfluoro-1-butanesulfonate,    -   2,2′-biphenylylene-diphenylantimony hexafluorophosphate,    -   2,2′-biphenylylene-diphenylantimony hexafluoroantimonate,    -   2,2′-biphenylylene-diphenylantimony        tetrakis(pentafluorphenyl)borate,    -   2,2′-biphenylylene-diphenylantimony        tris(trifluoromethanesulfonyl)methide,    -   2,2′-biphenylylene-diphenylantimony        hexafluoropropane-1,3-disulfonimide,    -   2,2′-biphenylylene-diphenylantimony        bis(trifluoromethenesulfonyl)amide,    -   bis(2,2′-biphenylylene-diphenylantimony)        perfluorbutane-1,4-disulfonate,    -   2,2′-biphenylylene-diphenylantimony        2-(trifluormethyl)benzenesulfonate,    -   tetraphenylbismuth camphorsulfonate,    -   tetraphenylbismuth p-toluenesulfonate,    -   tetraphenylbismuth trifluoromethenesulfonate,    -   tetraphenylbismuth perfluoro-1-butanesulfonate,    -   tetraphenylbismuth hexafluorophosphate,    -   tetraphenylbismuth hexafluoroantimonate,    -   tetraphenybismuth tetrakis(pentafluorphenyl)borate,    -   tetraphenylbismuth tris(trifluoromethanesulfonyl)methide,    -   tetraphenylbismuth hexafluoropropane-1,3-disulfonimide,    -   tetraphenylbismuth bis(trifluoromethenesulfonyl)amide,    -   bis(tetraphenylbismuth) perfluorbutane-1,4-disulfonate,    -   tetraphenylbismuth 2-(trifluormethyl)benzenesulfonate,    -   2,2′-biphenylylene-diphenylbismuth camphorsulfonate,    -   2,2′-biphenylylene-diphenylbismuth p-toluenesulfonate,    -   2,2′-biphenylylene-diphenylbismuth trifluoromethenesulfonate,    -   2,2′-biphenylylene-diphenylbismuth perfluoro-1-butanesulfonate,    -   2,2′-biphenylylene-diphenylbismuth hexafluorophosphate,    -   2,2′-biphenylylene-diphenylbismuth hexafluoroantimonate,    -   2,2′-biphenylylene-diphenylbismuth        tetrakis(pentafluorphenyl)borate,    -   2,2′-biphenylylene-diphenylbismuth        tris(trifluoromethanesulfonyl)methide,    -   2,2′-biphenylylene-diphenylbismuth        hexafluoropropane-1,3-disulfonimide,    -   2,2′-biphenylylene-diphenylbismuth        bis(trifluoromethenesulfonyl)amide,    -   bis(2,2′-biphenylylene-diphenylbismuth)        perfluorbutane-1,4-disulfonate, and    -   2,2′-biphenylylene-diphenylbismuth        2-(trifluormethyl)benzenesulfonate.

In a particular preferred variant, the photoacid generator according tothe present invention includes 2,2′-biphenylylene-diphenylbismuthcamphorsulfonate or 2,2′-biphenylylene-diphenylbismuthp-toluenesulfonate.

However, persons with an ordinary skill in the art will realize that inthe photoreactions described in detail above also other, i.e., modified,photoacid generator compound anions, e.g., substituted anions, complexanions, etc., can be used.

The synthesis of the PAG according to the present invention is describedexemplary for the PAG tetraphenylbismuth p-toluenesulfonate: Firsttriphenylbismuth is derived from BiCl₃ by substitution with threeequivalents of a phenyl lithium reagent in a tetrahydrofuran solvent ata temperature of −78° C. Thereafter triphenylbismuth is treated withthionyl chloride as an oxidizing agent in dichloromethane solvent at−78° C. to yield triphenylbismuth dichloride. Then tetraphenylbismuthchloride is produced from triphenylbismuth dichloride by displacement ofa Bi—Cl bond with a phenyl lithium reagent in tetrahydrofuran solvent at−78° C. Finally, tetraphenylbismuth p-toluenesulfonate is obtained bytreating tetraphenylbismuth chloride with a solution of silverp-toluenesulfonate. People with an ordinary skill in the art willrealize that other photoacid generators according to the presentinvention can be synthesized along the same lines.

Due to their distinguished properties as described above, the photoacidgenerator, comprising the photoacid generator compound cation accordingto the present invention, can be formulated into polymer compositionsthat are useful in lithographic processes, especially when EUVirradiation is used.

Hence, in a further aspect, the present invention relates to aphotoresist composition, comprising:

-   -   (a) a photoacid generator compound according to the present        invention; and    -   (b) an acid labile polymer.

The acid labile polymer is preferably capable of undergoing chemicaltransformations upon exposure of the photoresist composition, inparticular DUV irradiation or EUV irradiation, whereby a differential inthe solubility of the polymer in either the exposed regions or theunexposed regions is created. In such a polymer, the acid sensitivityexists because of the presence of acid sensitive side chains that arebonded to the polymer backbone. Such acid sensitive polymers includingacid sensitive side chains are conventionally.

The acid labile imaging polymer used according to the present inventionpreferably is selected from a copolymer such as poly(p-hydroxystyrene)-r-poly(t-butyl acrylate) and a terpolymer such aspoly(p-hydroxy styrene)-r-poly(styrene)-r-poly(t-butyl acrylate).

The content of the photoacid generator compound according to the presentinvention in the photoresist composition is preferably 1 to 30% byweight, and more preferably 5 to 20% by weight, based on the totalweight of the photoresist composition.

The photoresist compositions of the invention preferably contain asolvent which is capable of dissolving the acid sensitive imagingpolymer and the photoacid generator. Examples of such solvents include,but are not limited to, ethers, glycol ethers, aromatic hydrocarbons,ketones, esters and the like. A solvent system including a mixture ofthe aforementioned solvents is also contemplated herein. Suitable glycolethers include 2-methoxyethyl ether (diglyme), ethylene glycolmonomethyl ether, propylene glycol monomethyl ether, propylene glycolmonomethylether acetate (PGMEA) and the like. Suitable aromatichydrocarbon solvents include toluene, xylene, and benzene. Examples ofketones include methylisobutylketone, 2-heptanone, cycloheptanone, andcyclohexanone. An example of an ether solvent is tetrahydrofuran,whereas ethyl lactate and ethoxy ethyl propionate are examples of estersolvents that may be employed herein.

In addition to the above components, the photoresist composition mayalso include other components such as a base quencher, aphotosensitizer, a pigment, a filler, an antistatic agent, a flameretardant, a defoaming agent, a light stabilizer, an antioxidant, orother additives. If desired, combinations or mixtures of these othercomponents may be used.

Chemically amplified photoresists for EUV lithography that comprise thephotoacid generator compound cation and the photoacid generatoraccording to the present invention have a high absorption cross sectionfor photons in the EUV, and thus, have an increased sensitivity in theEUV.

Preferably, chemically amplified photoresists for EUV lithography thatcomprise the organobismuth photoacid generator described herein, whichhave a high absorption cross section for photons in the EUV, areparticularly appealing as they are the least toxic compounds among theheavy metals (Jingfei Luan, Lingyan Zhang and Zhitian Hu, Molecules, 16,4194 (2011)). Additionally, bismuth compounds have a cost advantage.Preferably, the embodiments of the fluorine-free photoacid generatorssuch as 2,2′-biphenylylene-diphenylbismuth camphorsulfonate and2,2′-biphenylylene-diphenylbismuth p-toluenesulfonate have a material'stoxicity and chemical waste advantage over, for example, organotin ororganoantimony compounds (taught in here, and in, for example, U.S. Pat.No. 10,642,153 for said inorganic photoresists), and fluorinatedphotoacid generators.

Chemically amplified photoresists for EUV lithography that comprise thephotoacid generator compound cation and the photoacid generatordescribed herein, also pose limited process-integration risks becausethe process flow in the fab's photobay is unchanged.

In a further aspect, the present invention also encompasses a method ofusing the photoresist composition of the invention for generating anacid. Said method comprises the steps: applying a photoresistcomposition (i.e., an embodiment of the present invention), containingthe photoacid generator according to the invention, to a substrate; andirradiating patternwise the photoresist composition with an energy rayto cause the photoacid generator to generate an acid.

As substrate in the present invention is suitable any substrateconventionally used in processes involving photoresists. For example,the substrate can be silicon, silicon oxide, aluminium, aluminium oxide,gallium arsenide, ceramic, quartz, copper or any combination thereof,including multilayers.

In a preferred variant of the method according to the present invention,the energy ray with which the patternwise irradiation of the photoresistcomposition is conducted, is a DUV irradiation or preferably an EUVirradiation.

In a further aspect, the present invention also encompasses a method forusing the photoresist composition of the invention to form patternedmaterial features on a substrate comprising a material surface which maycomprise a metal conductor layer, a ceramic insulator layer, asemiconductor layer or other material depending on the stage of themanufacture process and the desired material set for the end product.The photoresist composition of the invention is especially useful forEUV lithographic processes used in the manufacture of integratedcircuits on semiconductor substrates. The photoresist composition of theinvention used in lithographic processes create patterned material layerstructures such as metal wiring lines, holes for contacts or vias,insulation sections (e.g., damascene trenches or shallow trenchisolation), trenches for capacitor structures, ion implantedsemiconductor structures for transistors, and the like as might be usedin integrated circuit devices.

After exposure, the photoresist structure with the desired pattern isobtained or developed by contacting the photoresist layer with anaqueous alkaline solution which selectively dissolves the areas of thephotoresist which were exposed to radiation in the case of a positivephotoresist (or the unexposed areas in the case of a negativephotoresist). Some aqueous alkaline solutions or developers compriseaqueous solutions of tetramethyl ammonium hydroxide. The resultinglithographic structure on the substrate is then typically dried toremove any remaining developer. If a top coat has been used, it can bedissolved by the developer in this step.

The pattern from the photoresist structure may then be transferred tothe exposed portions of underlying material of the substrate by etchingwith a suitable etchant using techniques known in the art. In oneembodiment the transfer is done by reactive ion etching or by wetetching. Once the desired pattern transfer has taken place, anyremaining photoresist may be removed using conventional strippingtechniques. Alternatively, the pattern may be transferred by ionimplantation to form a pattern of ion implanted material.

In a preferred variant of the method according to the present invention,the energy ray with which the pattern-wise irradiation of thephotoresist composition is conducted, is a DUV irradiation or preferablyan EUV irradiation.

What is claimed is:
 1. A photoacid generator compound cation usingR_(n)−X⁺ wherein X represents an element (i) having for 92 eV photons(extreme ultraviolet (EUV)) an absorption cross section of at least0.5×10⁷·cm²/mol; (ii) having at least two stable oxidation states; and(iii) selected from the elements of group 1 to group 15 of the periodictable of the elements; R represents a linear or branched or a cyclicunsubstituted or substituted alkyl group having 1 to 20 carbon atoms; oran unsubstituted or substituted aryl group having 3 to 30 carbon atoms;or an unsubstituted or an substituted unsaturated or a saturatedheterocyclic group having a 3 to 30 membered ring; or derivativesthereof; wherein the R groups are either separated from each other or atleast two R groups are linked with each other; and n is 2 to
 5. 2. Thephotoacid generator compound cation according to claim 1, wherein the atleast two stable oxidation states are 1+and 3+; 2+and 4+; 3+and 5+; or4+and 6+.
 3. The photoacid generator compound cation according to claim1, wherein X is selected from the group consisting of the elements In,Sn, Sb, Tl, Pb, and Bi.
 4. The photoacid generator compound cationaccording to claim 1, wherein the linear or the branched alkyl group isselected from the group consisting of methyl, ethyl, butyl, pentyl,hexyl, heptyl, octyl, nonyl decyl, undecyl, dodecyl, tridecyl,tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl,icosayl and derivatives thereof; the cyclic alkyl group is selected fromthe group consisting of cyclopentane, cyclohexane, cycloheptane,cyclooctane and derivatives thereof; the aryl group is selected from thegroup consisting of phenyl, naphthyl and derivatives thereof; and thesaturated or unsaturated heterocyclic group having one or twoheteroatoms is selected from the group consisting of pyrrolidine,pyrrole, tetrahydrofuran, furan, tetrahydrothiophene, thiophene,imidazolidine, imidazole, oxazolidine, oxyzole, thiazolidine, thiazole,dioxolane, dithiolane, piperidine, pyridine, tetrahydropyran, pyran,thiane, thiopyran, diazinane, diazine, in particular pyridazin(1,2-diazin), pyrimidine (1,3-diazin) and pyrazin (1,4-diazin),morpholine, oxazine, thiomorpholine, thiazine, dioxane, dioxine,dithiane, dithiin, quinolone, isoquinoline and derivatives thereof. 5.The photoacid generator compound cation according to claim 1, whereinthe linear or the branched alkyl group is selected from the groupconsisting of methyl, ethyl, butyl, pentyl, hexyl, heptyl, octyl, nonyldecyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,heptadecyl, octadecyl, nonadecyl, icosayl and derivatives thereof; orthe cyclic alkyl group is selected from the group consisting ofcyclopentane, cyclohexane, cycloheptane, cyclooctane and derivativesthereof or the aryl group is selected from the group consisting ofphenyl, naphthyl and derivatives thereof; or the saturated orunsaturated heterocyclic group having one or two heteroatoms is selectedfrom the group consisting of pyrrolidine, pyrrole, tetrahydrofuran,furan, tetrahydrothiophene, thiophene, imidazolidine, imidazole,oxazolidine, oxyzole, thiazolidine, thiazole, dioxolane, dithiolane,piperidine, pyridine, tetrahydropyran, pyran, thiane, thiopyran,diazinane, diazine, in particular pyridazin (1,2-diazin), pyrimidine(1,3-diazin) and pyrazin (1,4-diazin), morpholine, oxazine,thiomorpholine, thiazine, dioxane, dioxine, dithiane, dithiin,quinolone, isoquinoline and derivatives thereof.
 6. The photoacidgenerator compound cation according to claim 1, wherein the alkyl groupor aryl group or heterocyclic group include at least one substituentselected from the group consisting of halogen, hydroxyl, alkyl, alkoxy,aryl, aryloxy, nitro, and cyano.
 7. The photoacid generator compoundcation according claim 1, wherein the at least two R groups are linkedvia a covalent bond between any of two C atoms of the two R groups or alinking atom or linking group, selected from the group consisting of—C—,—O—, —S—, —C(O)—, —S(O)-, and —S(O)₂-.
 8. The photoacid generatorcompound cation according to claim 1, wherein the photoacid generatorcompound cation is selected from the group consisting of triphenyltin,2,2′-biphenylylene-phenyltin, tetraphenylantimony,2,2′-biphenylylene-diphenylantimony, tetraphenylbismuth, and2,2′-biphenylylene-diphenylbismuth.
 9. The photoacid generatorcomprising the photoacid generator compound cation according to claim 1and an anion.
 10. The photoacid generator according to claim 9, whereinthe anion is selected from the group consisting of camphorsulfonate,p-toluenesulfonate, trifluoromethanesulfonate,perfluoro-1-butanesulfonate, hexafluorophosphate, hexafluoroantimonate,tetrakis(pentafluorophenyl)borate,tris(trifluoromethanesulfonyl)methide,hexafluoropropane-1,3-disulfonimide, bis(trifluoromethenesulfonyl)amide,perfluorobutane-1,4-disulfonate, 2-(trifluoromethyl)benzenesulfonate andderivatives thereof.
 11. The photoacid generator according to claim 10,wherein the photoacid generator is selected from the group consistingof: triphenyltin camphorsulfonate, triphenyltin p-toluenesulfonate,triphenyltin trifluoromethenesulfonate, triphenyltinperfluoro-1-butanesulfonate, triphenyltin hexafluorophosphate,triphenyltin hexafluoroantimonate, triphenyltintetrakis(pentafluorphenyl)borate, triphenyltintris(trifluoromethanesulfonyl)methide, triphenyltinhexafluoropropane-1,3-disulfonimide triphenyltinbis(trifluoromethenesulfonyl)amide, bis(triphenyltin)perfluorbutane-1,4-disulfonate, triphenyltin2-(trifluormethyl)benzenesulfonate, 2,2′-biphenylylene-phenyltincamphorsulfonate, 2,2′-biphenylylene-phenyltin p-toluenesulfonate,2,2′-biphenylylene-phenyltin trifluoromethenesulfonate,2,2′-biphenylylene-phenyltin perfluoro-1-butanesulfonate,2,2′-biphenylylene-phenyltin hexafluorophosphate,2,2′-biphenylylene-phenyltin hexafluoroantimonate,2,2′-biphenylylene-phenyltin tetrakis(pentafluorphenyl)borate,2,2′-biphenylylene-phenyltin tris(trifluoromethanesulfonyl)methide,2,2′-biphenylylene-phenyltin hexafluoropropane-1,3-disulfonimide,2,2′-biphenylylene-phenyltin bis(trifluoromethenesulfonyl)amide,bis(2,2′-biphenylylene-phenyltin) perfluorbutane-1,4-disulfonate,2,2′-biphenylylene-phenyltin 2-(trifluormethyl)benzenesulfonate,tetraphenylantimony camphorsulfonate, tetraphenylantimonyp-toluenesulfonate, tetraphenylantimony trifluoromethenesulfonate,tetraphenylantimony perfluoro-1-butanesulfonate, tetraphenylantimonyhexafluorophosphate, tetraphenylantimony hexafluoroantimonate,tetraphenylantimony tetrakis(pentafluorphenyl)borate,tetraphenylantimony tris(trifluoromethanesulfonyl)methide,tetraphenylantimony hexafluoropropane-1,3-disulfonimide,tetraphenylantimony bis(trifluoromethenesulfonyl)amide,bis(tetraphenylantimony) perfluorbutane-1,4-disulfonate,tetraphenylantimony 2-(trifluormethyl)benzenesulfonate,2,2′-biphenylylene-diphenylantimony camphorsulfonate,2,2′-biphenylylene-diphenylantimony p-toluenesulfonate,2,2′-biphenylylene-diphenylantimony trifluoromethenesulfonate,2,2′-biphenylylene-diphenylantimony perfluoro-1-butanesulfonate,2,2′-biphenylylene-diphenylantimony hexafluorophosphate,2,2′-biphenylylene-diphenylantimony hexafluoroantimonate,2,2′-biphenylylene-diphenylantimony tetrakis(pentafluorphenyl)borate,2,2′-biphenylylene-diphenylantimonytris(trifluoromethanesulfonyl)methide,2,2′-biphenylylene-diphenylantimony hexafluoropropane-1,3-disulfonimide,2,2′-biphenylylene-diphenylantimony bis(trifluoromethenesulfonyl)amide,bis(2,2′-biphenylylene-diphenylantimony) perfluorbutane-1,4-disulfonate,2,2′-biphenylylene-diphenylantimony 2-(trifluormethyl)benzenesulfonate,tetraphenylbismuth camphorsulfonate, tetraphenylbismuthp-toluenesulfonate, tetraphenylbismuth trifluoromethenesulfonate,tetraphenylbismuth perfluoro-1-butanesulfonate, tetraphenylbismuthhexafluorophosphate, tetraphenylbismuth hexafluoroantimonate,tetraphenybismuth tetrakis(pentafluorphenyl)borate, tetraphenylbismuthtris(trifluoromethanesulfonyl)methide, tetraphenylbismuthhexafluoropropane-1,3-disulfonimide, tetraphenylbismuthbis(trifluoromethenesulfonyl)amide, bis(tetraphenylbismuth)perfluorbutane-1,4-disulfonate, tetraphenylbismuth2-(trifluormethyl)benzenesulfonate, 2,2′-biphenylylene-diphenylbismuthcamphorsulfonate, 2,2′-biphenylylene-diphenylbismuth p-toluenesulfonate,2,2′-biphenylylene-diphenylbismuth trifluoromethenesulfonate,2,2′-biphenylylene-diphenylbismuth perfluoro-1-butanesulfonate,2,2′-biphenylylene-diphenylbismuth hexafluorophosphate,2,2′-biphenylylene-diphenylbismuth hexafluoroantimonate,2,2′-biphenylylene-diphenylbismuth tetrakis(pentafluorphenyl)borate,2,2′-biphenylylene-diphenylbismuthtris(trifluoromethanesulfonyl)methide,2,2′-biphenylylene-diphenylbismuth hexafluoropropane-1,3-disulfonimide,2,2′-biphenylylene-diphenylbismuth bis(trifluoromethenesulfonyl)amide,bis(2,2′-biphenylylene-diphenylbismuth) perfluorbutane-1,4-disulfonate,and 2,2′-biphenylylene-diphenylbismuth2-(trifluormethyl)benzenesulfonate.
 12. A photoresist compositioncomprising: a photoacid generator comprising a cation and an anion,wherein the anion is selected from the group consisting ofcamphorsulfonate, p-toluenesulfonate, trifluoromethanesulfonate,perfluoro-1-butanesulfonate, hexafluorophosphate, hexafluoroantimonate,tetrakis(pentafluorophenyl)borate,tris(trifluoromethanesulfonyl)methide,hexafluoropropane-1,3-disulfonimide, bis(trifluoromethenesulfonyl)amide,perfluorobutane-1,4-disulfonate, and2-(trifluoromethyl)benzenesulfonate; and an acid labile polymer.
 13. Thephotoresist composition according to claim 12, comprising the photoacidgenerator in an amount of 1 to 30% by weight, based on the total weightof the photoresist composition.
 14. A computer-implemented methodcomprising: generating an acid, wherein generating an acid comprises:applying a photoresist composition to a substrate; and irradiating thephotoresist composition with an energy ray to cause the photoacidgenerator to generate an acid.
 15. The computer-implemented methodaccording to claim 14, wherein the energy ray is a deep ultraviolet(DUV) irradiation or an extreme ultraviolet (EUV) irradiation.
 16. Thecomputer-implemented method of claim 14, further comprising: forming apatterned materials features on a substrate, wherein forming a patternedmaterials features on a substrate comprises: providing a materialsurface on a substrate; forming a layer of the photoresist compositionover said material surface; patternwise irradiating the photoresistlayer with an energy ray thereby creating a pattern of radiation-exposedregions in said photoresist layer; selectively removing portions of saidphotoresist layer to form exposed portions of said material surface; andetching or ion implanting said exposed portions of said material,thereby forming said patterned material feature.
 17. Thecomputer-implemented method according to claim 15, wherein the energyray is a deep ultraviolet (DUV) irradiation or an extreme ultraviolet(EUV) irradiation.